Diodes giving up the ghost - why?

stangbat

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I've been repairing a few machines and I've been surprised by the number of bad diodes on CPU controlled lamps. One game had four that were bad, just on the lamps, and they were all on different portions of the matrix. On other games I've had a few that were bad on some stand ups, a few other lamps here and there, but but I haven't run across a bad one on a coil yet. Seems like bad diodes are not all that uncommon but my question is why? It doesn't seem to me that they would be taking a beating on the lamp matrix. On the coils, especially the higher voltage coils, I could see them going out but that hasn't been the case with the machines I've come across.

Is this just a case of them being made cheaply? Is there more stress on them in the lamp matrix than I realize? Is there something inherent in a pinball machine that makes them go out quickly? Or have I just run across a string of problems and I may not see many bad ones for a while?
 
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In all the years I've worked on coin op machines, I've never come across bad lamp matrix diodes. Usually I find a bad lamp socket or a bad lamp driver transistor instead.

I see lots of broken diodes on coils, especially flipper coils.
 
Replaced another bad diode on a CPU controlled lamp today (different game). I think all these have been on DE games. Are DE games hard on the diodes or did they use cheap diodes?
 
I think I saw it from Clay that you should give a diode a good tug when working near them before testing. Seems when they fail it messes up their stength to stay together.

And when you can get 100 of them shipped for $4 off of ebay you have to question their quality.
 
I too have replaced many on a Flash I restored in its backbox lighting. All I repalced were melted/distored and I've no idea why...
 
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